Electrical drivetrain for work machine, such as a track type tractor, may typically include an engine (e.g., internal combustion engine), a generator coupled to the engine, a Direct Current (DC) power source and a motor. The DC power source may be coupled electrically between the generator and the motor to drive one or more ground engaging elements of the machine. A converter may be coupled electrically between the generator and the DC power source. The converter may be controlled to convert Alternating Current (AC) power to DC power when the generator generates power, and DC power to AC power when the generator utilizes power to drive the motor. An inverter may be coupled electrically between the DC power source and the motor. The inverter may be configured to convert DC power from the DC power source to AC power when the generator utilizes power to drive the motor and to convert AC power to DC power during electrical braking of the motor.
The motor may be a switched reluctance (SR) motor. Traditionally, the SR motor has been controlled using open-loop table-based control. However, this type of control cannot compensate for the dynamic variants in the system, such as the DC-link voltage or phase currents of the phases of the SR motor. This is due to the fact that control tables are tuned or calculated as a function of test stand setup at a fixed DC-link voltage. If, in practice, the DC-link voltage departs from that voltage, or the actual phase current has drifted from the commanded phase current, the actual torque generated by the SR motor may deviate substantially from a requested torque.
In order to account for variations in the DC-link voltage, control maps developed off-line should include an axis for the DC-link voltage. This requirement increases required memory space at a rate proportional to number of voltages points considered, besides needing a higher-dimensional interpolation algorithm in order to account for the extra dimension. A higher DC-link voltage decreases the reliability and/or accuracy of an initial position algorithm of the SR motor. Due to lower accuracy of the initial position algorithm, the risk of lower torque accuracy increases even further. Also, part-to-part variations in the SR motor manufacturing increases risk of torque accuracy error. Torque tuning process is costly and time consuming, but currently needed every time a new design is implemented. On a SR motor where speed is controlled to a speed target, adjusting torque output directly based on an algorithm can make tuning the speed control difficult. Further, if the torque limit is set too high, damage to mechanical and electrical components can occur. On the other hand, if the torque limit is set too low, motor performance is degraded
Thus, an improved control means for the SR motor is required.